1. Field of the Invention
On boats and ships, and in particular on single screw vessels, the non-uniform flow of water to the propeller presents a problem. In other words, the strength and direction of the flow to the propeller can vary to some degree (more or less significantly) in the area of the propeller blades. Such a situation can result due to the deflection of the flow around the ship's hull ahead of the propeller, which may not have the same shape as the propeller shaft.
2. Description of the Prior Art
The propulsion disadvantages which result from this lack of uniformity are numerous, however, and provide the impetus for the present invention. The following phenomena can be considered resulting disadvantages:
a. Reductions in the efficiency of the thrust produced, since the propeller may not always receive the flow at an optimum angle;
b. Vibrations produced by the propeller blades not receiving a uniform flow during one revolution of the propeller, resulting in periodic pressure pulses on the propeller surface and the external skin of the vessel;
c. Cavitation and erosion of the propeller blades: and
d. Propeller noise.
Almost the only means known in the prior art to eliminate these disadvantages is to provide guide surfaces or nozzles in the immediate vicinity of the propeller, close ahead of the propeller and in the area of the mountings on the hull. See, for example, DE-PS No. 24 41 556. In contrast to the guide surfaces and nozzles of the prior art immediately ahead of the propeller, the present invention provides that the flow to the propeller be influenced far ahead of the propeller, because then the same effect can be achieved with smaller deflection angles and a lower resistance.
U.S. Pat. No. 4,746,314, issued May 24, 1988 and entitled "Combined Propulsion and Steering System for a Motor Boat with an Inboard Engine"; U.S. Pat. No. 4,756,265, issued July 12, 1988 and entitled "High Speed Boat Lifting Structures": U.S. Pat. No. 4,689,026, issued Aug. 25, 1987 and entitled "Propeller Tunnel Baffle and Method": U.S. Pat. No. 4,672,905, issued June 16, 1987 and entitled "Boat Hull with Center V-Hull and Sponsons": U.S. Pat. No. 4,629,432, issued Dec. 16, 1986 and entitled "Elastically Supported Thruster Structure"; U.S. Pat. No. 4,406,635, issued Sept. 27, 1983 and entitled "Marine Vessel with at Least One Propeller"; and U.S. Pat. No. 4,004,534, issued Jan. 25, 1987 and entitled "Boat Hull" are all examples of prior art which relate to ships or vessels employing propeller propulsion and/or having fluid deflection surfaces, and the technical concerns relating thereto.
All of the above mentioned prior art documents are hereby expressly incorporated by reference, with the same effect as if set forth in their entireties herein.